Process for providing an article with a porous resinous coating and the coating composition



United States Patent Int. 01. 1354a 1/44 US. Cl. 117-63 8 Claims ABSTRACT OF THE DISCLOSURE A process for providing smooth surfaced articles with a porous foam of a thermoplastic resin by treating said articles with a mixture of a solution of a thermoplastic resin in a water-miscible organic solvent and a water-immiscible solvent, said mixture having a viscosity of 100 to 1,000 cps. and vaporizing the water-immiscible solvent in a hot water bath while simultaneously hardening the resin and the articles produced by the said process.

PRIOR ART Various attempts have been made to improve the quality of light-weight paper articles and non-woven fabrics such as coating thin cellulose fabrics with binders in foam form in the paper making, filling reenforced fiber fabrics with urea-resin foam flakes, needled 0r backed with cellulose cotton fabrics, etc. When these smoothsurfaced articles are to be used for hygienic purposes, they have to possess a distinct capacity for absorbing and retaining aqueous liquids while at the same time possessing woven-like qualities such as softness, yield, feel, satisfactory strength even when wet and an ability to resist temperature and light influences, particularly when they are used for textile purposes.

OBJECTS OF THE INVENTION It is an object of the invention to provide novel articles having excellent water absorption properties and fibrouslike surface qualities.

It is a further object of the invention to provide novel compositions for coating smooth-surface articles to give them a fiber-like surface.

It is another object of the invention to provide a process for treating smooth-surface papers and non-woven fabrics and fibers with a porous, fibrous-like surface.

These and other objects and advantages of the invention will become obvious from the following detailed description.

THE INVENTION The process of the invention for providing smooth surface articles of natural or synthetic fibers such as paper and non-woven, Woven or knitted fabrics with fibrous-like surfaces comprises applying to the said smooth-surfaced articles a mixture of a water-immiscible, low boiling organic solvent and a solution of a thermoplastic resin in a water-miscible organic solvent and passing the said article through hot water to simultaneously vaporize the water-immiscible solvent and harden the polymer and drying the articles to obtain articles having a fibrous-like, porous surface.

Surprisingly, the smooth surface articles are provided with a porous foam of a thermoplastic resin which results because the polymers harden simultaneously with the gas evolution from the evaporation of the water-immiscible, low boiling solvent. Prior methods of coating "ice textiles with resins allowed the resin to begin to harden before foaming. A more or less thick film which gives a leathery, usually stiff, impermeable, non-textile appearance to the textile has always resulted from the processes. According to all previous experiences, a porous coating was thought to be obtained only when a closed film prevented the premature escape of the gaseous vapors and, therefore, a process which avoided the prior art disadvantages was not believed feasible. Coatings obtained according to the process do not only have film on the surface but are especially porous and fiber-like on the surface.

The process of the invention requires the use of a liquid or plastic composition for coating the article and after the application, usually done by heating, the coating must give off a blowing gas (vapor of the evap rated water-immiscible, low boiling solvent) and at the same time must coagulate and harden with corresponding speed. The necessary simultaneous coagulation and hardening is effected by using polymers which precipitate from water-miscible solvents in the presence of excess Water. The blowing gas expands already precipitated pore membranes, particularly in the surface nearest the boundary layer, to the bursting point which reduces the membranes to fiber-like fragments which adhere firmly to each other.

The compositions of the invention used for the process of the invention are comprised of a mixture of a solution of 5 to 35 gm. of a thermoplastic resin per 100 ml. of a. water-miscible organic solvent and a water-immiscible, low boiling organic solvent, the latter being present in sufficient amount to produce at least 0.2 to 1.5 liters of gas per gram of polymer and the said mixture having a viscosity of 100 to 10,000 c.p.s. depending upon the absorptivity of the base to be coated.

Suitable thermoplastic resins suitable for the invention are polymers which are precipitated from water-miscible solutions in the presence of excess water. Examples of said polymers are polyamides such as polyhexamethyleneadipamide, polyamidodecamethylene-carboxylic acid, etc., polycaprolactam, polyacrylonitrile, polyvinyl acetate, polyvinylacetals, etc. and copolymers thereof.

Examples of suitable water-miscible organic solvents suitable for forming solutions of the thermoplastic resin are lower alkanols such as methanol, ethanol, etc.; dilower-alkyl lower alkanolic acid amides such as dimethylformamide; dimethylsulfoxide, heterocyclics such as tetrahydrofuran, etc. Lower alkanols saturated with a nitrate or halide-of alkaline earth metals and alkali metals such as magnesium, calcium and lithium, preferably methanol saturated with calcium chloride are preferred solvents for polyamides and polymers of epsilonamide and dimethylsulfoxide are preferred solvents for polyacrylonitrile and ethanol and tetrahydrofuran are preferred solvents for polyvinyl acetates and polyvinylacetals.

The low boiling, water-immiscible organic solvents must have a boiling point below 100 C., i.e., 10 to 95 C., preferably C. Examples of said solvents are hydrocarbons such as pentane, hexane, benzene, etc.; halogenated hydrocarbons such as methylene chloride, chloroform, dichlorodifluoromethane, etc.; hydrocarbon ethers such as ethyl ether, etc.; and lower carboxylic acid esters or mixtures thereof. The said low boiling solvents must be water-immiscible or water-insoluble or only filmy coatings are formed which are relatively hard to the touch and poor in absorption and heat and light resistance due to their high apparent densities. caprolactam, and copolymers thereof. Dimethylform- The compositions of the invention may contain other 3 known additives to obtain special effects such as other polymers, dyes, softening agents, wetting agents, nonabsorbent agents, anti-adhesive agents, dirt-resistant agents, biocides, textile aids, etc.

Examples of the smooth surface articles to be coated by the process of the invention are textiles, particularly those with a very loose weave texture such as tulle, mull, muslin, etc., non-woven textiles which can be produced by wet process, mechanically or pneumatically and which are solidified in more or less large sizes, smooth or crepe papers made of short fibers such as 3 to 6 mm. or of long fibers such as to 100 mm.

The temperature of the water bath into which the treated articles are dipped for a short time to effect simultaneous evaporation of the low boiling solvent and solidification of the polymer may vary from 20 to 100 C., preferably from to 100 C. depending upon the boiling point of the low boiling solvent. For example, with certain fluorohydrocarbons the water bath temperature may be about room temperature but the use of hydrocarbons or chlorinated hydrocarbons with boiling points of 30 to 70 C. are preferred and bath temperatures of 50 to 100 C. are suitable for these solvents.

The water bath may also contain additives for special effects such as the ones described above for the coating compositions as well as flame retardants, fungicides, bactericides, hydrophilic compounds, crease-proofing agents, agents to effect the coagulation of the polymer, etc.

After the water bath, the treated articles are squeezed to remove excess water and then dried. If desired, special effects can be obtained during drying by temperature and/or pressure control.

Various methods have been suggested for the preparation of polymer foams but have disadvantages. German Patent No. 1,002,124 and No. 1,109,880 subject solutions of polyamides in strong mineral acids to treatment with alkali metal carbonate solutions but these methods must use strong acids which cause rapid hydrolytic decomposition of polyamides and which will damage the basic articles being treated in the process of the invention. German Patent No. 1,159,643 discloses the formation of foams of polymerized lactams directly and not from a solution which gives foams of relatively high apparent densities, closed pores and an impermeable film.

The process of the invention has the advantage of being effected with solutions which do not effect the material being treated nor decompose the polymer and gives firmly adhering, but excessively light foams consisting almost entirely of open pores. When viewed with moderate magnification, the treated articles of the invention look like Iceland Moss but is a composite of fibrous particles firmly attached and secured to each other as well as the original article treated.

To impregnate or coat the articles being treated, known processes such as padding and doctoring methods may be used depending on whether the application is unilateral or multilateral. An air brush may also be used in some instances but it has limited application due to the pres ence of the low boiling solvents.

The coated articles produced by the process of the invention may be used for a variety of purposes such as covering or supporting layers for hygienic articles, clothing subjected to heavy soilage such as aprons, smocks, gloves, work clothes, dressing jackets, cleaning rags, etc. Depending upon the base material and the amount of polymer, the products may be for one-time use or may be washable for re-use. Because of their highly porous form, the products are often superior to textile fabrics made from the same polymers for physiological clothing.

In the following examples there are described several preferred embodiments to illustrate the invention. However, it should be understood that the invention is not intended to be limited to the specific embodiments.

4 EXAMPLE I 20 mm. of polyacrylonitrile were dissolved with stirring in 100 ml. of dimethylformamide while heating in a water bath and after cooling the solution to room temperature, a mixture of 50 ml. of diethyl ether and 33 ml. of dimethylformamide was added while stirring. This composition 'was filtered through a fine-mesh bronze screen to remove the undissolved matter and the composition had a dynamic viscosity of about 3000 cp. A non-woven fabric weighing 30 gm./qm. was impregnated with the composition by padding it between a pair of horizontal rollers having the said composition disposed therebetween whereby a wet application of about gm./qm. was obtained. The fabric ribbons was guided from above so that it was immersed as soon as possible after the discharge from the roller slit into a waterbath heated to 75 C. placed beneath the pair of rollers for the purpose of foaming. After a bath travel of at least 25 cm., it was drawn over a guide roller and the product was washed with water to remove residual salts. The largest amount of the water was eliminated by squeezing the product between rubber rollers to to 120% of residual moisture. After drying, the fabric was smoothed out by ironing.

EXAMPLE II 15 gm. of polycaprolactam were dissolved with ml. of a solution of 18 gm. of dehydrated calcium chloride in 100 ml. of methanol and the mixture was admixed with 6 ml. of methylene chloride. The solution then showed a dynamic viscosity of about 1,000 cps. and was filtered through a fine-mesh bronze screen to remove undissolved matter. Application and foaming were effected on a non-woven fabric as described in Example 1.

EXAMPLE III 15 gm. of polyhexamethyleneadipamide were dissolved in 100 ml. of a solution of 18 gm. of dehydrated calcium chloride in 100 ml. of methanol and the mixture was cooled with ice water to 5 to 8 C. While stirring, 7.5 ml. of cooled difiuorodichloromethane were added thereto and the mixture was immediately afterwards used for coating a muslin fabric weighing 38 gm. The layer thickness was adjusted so that a wet application of about 80 gm. was obtained. Foaming was effected as described in Example I.

EXAMPLE IV 15 gm. of polycaprolactam were dissolved in 100 ml. of a solution of 18 gm. of dehydrated calcium chloride in 100 ml. of methanol and the mixture was admixed with 20 ml. of methylene chloride to obtain a solution having a dynamic viscosity of 480 cps. Crepe-paper ribbon, resting on a 0.8 mm. thick polyvinyl chloride foil was coated with this solution by passing it through the application rollers and the hot-water bath of Example I. Then the ribbon was secured so that it could be wound separately and could be further processed as described in Example I.

Various modifications of the articles and process of the invention may be made without departing from the spirit or scope thereof.

We claim:

1. A process for providing smooth surface articles made of synthetic and natural fibers with fibrous-like surfaces which comprises applying to the said smooth surface articles a mixture of a water-immiscible, low boiling organic solvent and a solution of a thermoplastic resin in a water-miscible organic solvent, said mixture having a viscosity of 100 to 10,000 cps., passing the said treated article into a water bath at temperatures high enough to simultaneously vaporize the low boiling solvent and harden the said resin and drying the articles to obtain articles having a fibrous-like, porous surface.

2. The process of claim 1 wherein the water-immiscible solvent has a boiling point of to 95 C.

3. A process for proving smooth-surface articles made of synthetic and natural fibers with a fibrous-like, porous surface which comprises applying to said smooth surface articles a mixture consisting essentially of a waterimmiscible, low-boiling organic solvent and a solution of polyhexamethyleneadipamide in methanol saturated with calcium chloride, said mixture having a viscosity of 100 to 10,000 cps, passing the said treated article into a water bath at temperatures high enough to simultaneously vaporize the low boiling solvent and harden the said resin and drying the article to obtain articles having a fibrous-like, porous surface.

4. A process for providing smooth-surface articles made of synthetic and natural fibers with a fibrous-like, porous surface which comprises applying to said smooth surface articles a mixture consisting essentially of a water-immiscible, low-boiling organic solvent and a solution of polyacrylonitrile in dimenthylformamide, said mixture having a viscosity of 100 to 10,000 cps., passing the said treated article into a water bath at temperatures high enough to simultaneously vaporize the low boiling solvent and harden the said resin and drying the article to obtain articles having a fibrous-like porous surface.

5. A process for providing smooth-surface articles made of synthetic and natural fibers with a fibrous-like, porous surface which comprises applying to said smooth surface articles a mixture consisting essentially of a water-immiscible, low-boiling organic solvent and a solution of polycaprolactam in methanol saturated with calcium chloride, said mixture having a viscosity of 100 to 10,000 cps., passing the said treated article into a water bath at temperatures high enough to simultaneously vaporize the low boiling solvent and harden the said resin and drying the article to obtain articles having a fibrouslike, porous surface.

6. A composition consisting essentially of a mixture of a solution of 5 to 35 gm. of polyhexarnethyleneadipamide per ml. of methanol saturated with calcium chloride and a water-immiscible, low-boiling organic solvent in sufficient amount to produce at least 0.2 to 1.5 liters of vapor per gram of resin, the said mixture having a viscosity of 100 to 10,000 cps.

7. A composition consisting essentially of a mixture of a solution of 5 to 35 gm. of polyacrylonitrile per 100 m1. of dimethylformamide and a water-immiscible, low boiling organic solvent in suificent amount to produce at least 0.2 to 1.5 liters of vapor per gram of resin, the said mixture having a viscosity of 100 to 10,000 cps.

8. A composition consisting essentially of a mixture of a solution of 5 to 35 gm. of polyycaprolactam per 100 ml. of methanol saturated with calcium chloride and a water-immiscible, low boiling organic solvent in sufiicient amount to produce at least 0.2 to 1.5 liters of vapor per gram of resin, the said mixture having a viscosity of 100 to 10,000 cps.

References Cited UNITED STATES PATENTS 2,359,877 10/1944 Schupp 260-334 2,359,878 10/1944 Schupp 26029.2 3,055,297 9/1962 Leeds 26033.4 X 3,100,721 8/1963 Holden l17l35.5

WILLIAM D. MARTIN, Primary Examiner T. G. DAVIS, Assistant Examiner US. Cl. X.R. 

